Active modified hedgehog proteins

ABSTRACT

The present invention provides isolated highly active hedgehog proteins esterified with a fatty acid having from 14 to 20 carbon atoms at the N-terminal domain of the protein. The highly active hh proteins are particularly useful therapeutic agents for treating bone disorders and neurodegenerative diseases. Methods for obtaining the highly active modified hedgehog proteins are also provided.

FIELD OF THE INVENTION

The invention concerns an active form of a hedgehog protein, a processfor its recombinant production and its therapeutic use.

BACKGROUND OF THE INVENTION

Hedgehog (hh) proteins are understood as a family of secreted signalproteins which are responsible for the formation of numerous structuresin embryogenesis (J. C. Smith, Cell 76 (1994) 193-196, N. Perrimon, Cell80 (1995) 517-520, C. Chiang et al., Nature 83 (1996) 407, M. J. Bitgoodet al., Curr. Biol. 6 (1996) 296, A. Vortkamp et al., Science 273 (1996)613, C. J. Lai et al., Development 121 (1995) 2349). During itsbiosynthesis a 20 kD N-terminal domain and a 25 kD C-terminal domain areobtained after cleavage of the signal sequence and autocatalyticcleavage. The N-terminal fragment is modified in its natural form withcholesterol at its C-terminus (J. A. Porter et al., Science 274 (1996)255-259). In higher life-forms the hh family is composed of at leastthree members i.e. sonic, indian and desert hh (Shh, Ihh, Dhh; M. Fietzet al., Development (Suppl.) (1994) 43-51). Differences in the activityof hedgehog proteins that were produced recombinantly were observedafter production in prokaryotes and eukaryotes (M. Hynes et al., Neuron15 (1995) 35-44 and T. Nakamura et al., Biochem. Biophys. Res. Comm. 237(1997) 465-469.

Hynes et al. compare the activity of hh in the supernatant oftransformed human embryonic kidney 293 cells (eukaryotic hh) with hhproduced from E. coli and isolated from the cytoplasm and find afour-fold higher activity of hh from the supernatants of the kidney cellline. A potential additional accessory factor which is only expressed ineukaryotic cells, a post-translational modification, a differentN-terminus since the hh isolated from E. coli contains 50% of a hh whichcarries two additional N-terminal amino acids (Gly-Ser) or is shortenedby 5-6 amino acids, or a higher state of aggregation (e.g. by binding tonickel agarose beads) have been discussed to be the reason for thisincreased activity.

Nakamura et al. compare the activity of shh in the supernatant oftransformed chicken embryo fibroblasts with an shh fusion proteinisolated from E. coli which still has an N-terminal polyhistidine part.The shh in the supernatant of the fibroblasts has a seven-fold higheractivity than the purified E: coli protein with regard to stimulation ofalkaline phosphatase (AP) in C3H10T ½ cells. Molecules such as bonemorphogenetic proteins (BMPs) have been discussed as the reason for theincreased activity which are only present in the supernatant ofeukaryotic cells and cause the stronger induction of AP.

Kinto et al., FEBS Letters, 404 (1997) 319-323 describe that fibroblastswhich secrete hh induce ectopic bone formation in an i.m. implantationon collagen.

SUMMARY OF THE INVENTION

The object of the invention is to produce hh proteins (polypeptides)which have a considerably improved activity compared to the known forms.In accordance with the present invention, the highly active hh proteinsare particularly useful for inducing or stimulating chondrocytes andosteocytes as well as for treating neurodegenerative diseases. Thus, thehighly active hh proteins of the present invention are usefultherapeutic agents for treating bone disorders such as, for example,osteoporosis and bone fractures.

In accordance with the present invention, a method is provided forobtaining isolated highly active post-translationally processed hedgehogprotein mutants (hh mutant) which are esterified with a fatty acidhaving from 14 to 20 carbon atoms (i.e., C₁₄-C₂₀) at the N-terminaldomain of the protein. The highly active hh proteins of the presentinvention are produced by expression of a gene which encodes a hedgehogprotein using a baculovirus expression system in a fermentation mediumcapable of producing the esterified hedgehog protein wherein thefermentation period is up to 30 hours, preferably from about 24 to about27 hours.

Isolation of the hh mutant from the fermentation supernatent can beobtained by conventional protein isolation techniques such as throughbinding of the hh protein to heparin-Sepharose and hydroxylapatite.Purification of the fermentation supernatant is preferably performed inthe presence of a protease inhibitor and a non-ionic detergent

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot showing the kinetics of the secretion of alkalinephosphatase (AP) inducing activity (bars) and shh protein (dots andline) by High Five cells after infection with baculovirus (t=0).

FIG. 2 is an elution diagram of the purification of the fermentationsupernatant with heparin-Sepharose.

FIG. 3 is an elution diagram of the purification of the dialyzed eluateof the heparin-Sepharose with hydroxylapatite.

FIG. 4 is an elution diagram of the purification of the dialyzed activefractions of the hydroxylapatite column with a 1 ml HiTrap heparincolumn.

FIG. 5 shows the alkaline phosphatase inducing activity of the fractionsof the 1 ml High Trap heparin chromatography.

FIG. 6 shows coomassie staining of SDS-PAGE with alkylated fractions ofthe 1 ml High Trap heparin chromatography.

FIG. 7 is a Western blot with an antibody against the N-terminus of shhof the SDS-PAGE with alkylated samples of the fractions of the 1 ml HighTrap heparin chromatography.

FIG. 8 is a Western blot with an antibody against the N-terminus of shhof the SDS-PAGE with reducing samples of the fractions of the 1 ml HighTrap heparin chromatography.

FIG. 9 shows the influence of suramin on the activity of the hh mutant:No suramin (B), suramin ad 0.1 mg/ml only added after dialysis againstPBS+0.05% Tween®80 or (C) suramin ad 0.1 mg/ml added before dialysis anddialysed against PBS+0.05% Tween®80 containing additionally 0.1 mg/mlsuramin (D) were added to aliquots of an active fraction afterhydroxylapatite chromatography. The AP activity in the absence of hh isshown by (A).

FIG. 10 shows the influence of Tween®20 and Tween®80 on the activity ofthe hh mutant: Aliquots of a pool of AP active fractions after SPSepharose chromatography in 50 mM NaPi, 0.9 M NaCl, 1 mM EDTA pH 7.3were admixed with the stated concentrations of Tween and dialysedagainst PBS containing the respective concentration of Tween. Thesamples were sterile filtered through 0.2 μm filters before being usedin the C3H10T½ test.

FIG. 11 shows the influence of trypsin and chymotrypsin on the activityof the hh mutant: AP active fractions after a step elution ofheparin-Sepharose were adjusted to a protein concentration of 0.46 mg/mlin 10 mM Na phosphate, 0.05% Tween®80 and admixed with trypsin orchymotrypsin at a protease/protein ratio (w/w) of 1:100 (A), 1:500 (B),1:2500 (C) and 1:10000 (D). The samples were incubated for 11 h at RT.The digestion was stopped by adding aprotinin in a 5-fold weight excessand the samples were analysed in SDS-PAGE (A:) and in the C3H10T½ test(B:). 1, test mixture; 2, control without protease; 3, samples treatedwith trypsin; 4, samples treated with chymotrypsin; 5, control trypsin(1:100) and aprotinin at t=0; 6, control chymotrypsin (1:100) andaprotinin at t=0.

FIG. 12 is an elution diagram of the purification of dialysed activefractions of the hydroxylapatite column with a 1.7 ml Poros HS/M column.The UV-detected elution diagram is shown as a line and the activities ofthe fractions in the cell test are shown as bars.

FIGS. 13A and 13B are elution diagrams of the separation of the activefractions of the Poros HS/M column by means of RP-HPLC.A.: Elutiondiagram of 10 to 75 min. detected at 220 nm. B: Elution diagram of 15 to40 min. detected at 280 nm.

FIG. 14 is an elution diagram of the purification of the dialysed activefractions of the hydroxylapatite column with a 6 ml Poros Q column. TheUV signal of the elution is shown as a line, the activity in the celltest as bars.

FIG. 15 shows the stability of the alkaline phosphatase inducingactivity towards dithiothreitol.

FIG. 16 shows the stability of the alkaline phosphatase inducingactivity towards hydroxylamine.

FIG. 17 shows MALDI mass spectra of the active modified hh derivativeafter RP-HPLC. A, B: Spectra obtained with different laser energies andfrom different spots.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides isolated highly active hedgehog proteinshaving a molecular weight of from about 19 to about 26 kD which areesterified with a fatty acid having from 14 to 20 carbon atoms at theN-terminal domain of the protein. Esterification of the hedgehog proteinwith a C₁₆ fatty acid is preferred.

In accordance with the present invention, the highly active hh proteinsare particularly useful for inducing or stimulating chondrocytes andosteocytes as well as for treating neurodegenerative diseases. Thus, thehighly active hh proteins of the present invention are usefultherapeutic agents for treating bone disorders such as, for example,osteoporosis and bone fractures.

The method of the present invention for producing the highly activehedgehog proteins esterified with a fatty acid having from 14 to 20carbon atoms comprises (a) providing an insect cell containing abaculovirus vector having a gene inserted therein capable of expressinga hedgehog protein, and a fermentation medium such that the insect celland medium are capable upon fermentation of producing a fatty acidhaving from 14 to 20 carbon atoms; (b) fermenting the insect cell in themedium for a period of about 30 hours or less to produce the fatty acidand express the hedgehog protein esterified with the fatty acid; and (c)isolating the esterified hedgehog protein from the protein producedduring the fermentation.

Any fermentation conditions which allow the esterification of thehedgehog protein with a fatty acid having from 14 to 20 carbon atoms canbe utilized. Preferably, the fermentation period is from about 24 toabout 27 hours. Generally, the fermentation is carried out at from about10 to 35° C. and pH of about 4 to 8. Fermentation at room temperatureand neutral pH is preferred. Any conventional medium for fermentation ofthe baculovirus expression system that allows the esterification of thehh protein can be utilized. A preferred fermentation medium is Excell400 medium (JHR, Inc.).

Isolation of the esterified hh protein can be obtained by conventionaltechniques for isolation of proteins such as through binding of the hhprotein to heparin-Sepharose and hydroxylapatite. The hedgehog proteinsof the present invention can be further purified by techniques such asanion or cation exchange chromatography and reverse-phase HPLC.Purification of the cell supernatant is preferably performed in thepresence of a protease inhibitor and a non-ionic detergent.

Hedgehog proteins are known and any hedgehog protein can be modified inaccordance with this invention to esterify the protein at the N-terminaldomain with a fatty acid having from 14 to 20 carbon atoms and in sodoing provide the highly active hh proteins of the present invention.

The esterified hedgehog proteins of the present invention have thefollowing characteristics:

-   -   exhibit an apparent molecular weight of 22±2 kDa under        alkylating conditions in SDS-PAGE,    -   exhibit an apparent molecular weight of 24±2 kD under reducing        conditions in SDS-PAGE,    -   are stabilized with respect to its activity by suramin    -   are inactivated when 8 or more amino acids are cleaved        N-terminally    -   are inactivated by 90% or more when incubated with 10 mmol/l 1.4        dithioerythritol (DTE) for 2.5 hours at preferably pH 8 and 37°        C.,    -   induce an activity for alkaline phosphatase of ca. 90 nmol        pNP/min/mg at a concentration of 5 nmol/l in the presence of        suramin,    -   are not modified by cholesterol (C-terminal) and    -   have at least 50-fold activity compared to the recombinant hh        protein isolated from the cytoplasm of E. coli. Activity within        the sense of the invention is understood as the activity of        alkaline phosphatase which the polypeptide can induce in        mammalian cells (activity in the alkaline phosphatase test). In        this method a mouse fibroblast cell line is cultured in a medium        which contains foetal calf serum. Subsequently sterile filtered        sample is added, the cells are lysed after ca. 5 days and        alkaline phosphatase is determined in the cell lysate by means        of the cleavage of a chromogenic substrate (pNP, p-nitrophenol)        (J. Asahina, Exp. Cell. Res. 222 (1996) 38-47 and T. Nakamura        (1997)).

A baculovirus expression system is understood as an expression systemcomposed of a baculovirus vector and an insect cell as the host cell.Such expression systems are known to a person skilled in the art and arefor example described by Bumcrot (1995) for hh proteins. Preferredinsect cells for use in obtaining the esterified hedgehog proteins ofthe present invention are High five cells.

A hedgehog protein is understood by the invention as a secreted signalprotein which is responsible for the formation of numerous structures inembryogenesis. Sonic, indian or desert hh proteins are particularlypreferably used (M. Fietz et al. (1994). A hh protein with a sequence asdescribed in the EMBL database under the No. L38518 is preferably used.Proteins of the hedgehog family exhibit a pronounced homology in theiramino acid sequence which is why it is also preferable to express thosenucleic acids which code for hedgehog proteins which are 80% or morehomologous with the above-mentioned sequence of sonic hedgehog protein.

The human sonic hedgehog precursor protein is composed of the aminoacids 1-462 of the sequence described in the EMBL database under No.L38518. The amino acids 1-23 represent the signal peptide, the aminoacids 24-197 represent mature signal domain, the amino acids 32-197represent the signal domain shortened by 8 amino acids and the aminoacids 198-462 represent the auto-processing domain after autoproteolyticcleavage. Thus, amino acids 24-197 of the human sonic hedgehog proteindescribed in EMBL database sequence No. L38518 represent the N terminaldomain of this sequence.

The first 8 amino acids of the hedgehog proteins of the presentinvention are the first 8 amino acids of the processed hedgehog protein,for example, the amino acids Cys24-Gly31 of the sequence described inthe EMBL database under No. L38518 for sonic hedgehog protein. Since themodified group can be cleaved with the first N-terminal amino acids ofhedgehog protein and the activity is greatly reduced by incubation withhydroxylamine or DTE, the binding of the group is localized on theseamino acids preferably in the form of a thioester, preferably aspalmitic acid thioester, on the cysteine which is present in the firsteight amino acids of the hedgehog protein.

Surprisingly when preferably the N-terminal domain of hedgehog proteinis produced recombinantly in the baculovirus expression system, a highlyactive form of the protein (activity increased by at least 10-fold,preferably at least 100-fold compared to recombinant shh from thecytoplasm of E. coli) accumulates in the initial period of thefermentation. However, overall the amount of highly active hh mutantaccording to the invention is only about 0.2-5% of the total protein inthe supernatant of the cells after expression in the baculovirusexpression system. This mutant of the polypeptide according to theinvention can be in particular isolated when the fermentation isterminated at the latest after about. 30 hours or less, preferably afterabout 24-27 hours. This is also surprising since a fermentation periodafter infection of at least 2 days has been previously described for theproduction of hh proteins in the baculovirus expression system (Bumcrotet al., Mol. Cell. Biol. 15 (1995) 2294-2303). It has also beendescribed for other proteins which are produced in the baculovirussystem such as rhodopsin kinase (Cha et al., Proc. Natl. Acad. Sci. USA94 (1997) 10577-10582) that a maximum of protein and activity isachieved after 64-88 h. According to the invention it was found forhedgehog proteins that although the amount of hedgehog protein in thefermentation supernatant greatly increases in the period between 33 and72 hours, mainly hh protein with an activity that is known from theprior art is formed in this period. In contrast the amount of such a hhprotein is considerably less (at least 3-5-fold) when the fermentationperiod is reduced to below ca. 30 h. which allows the identification andisolation of the highly active hh protein mutant according to theinvention.

The molecular weight of the mutant according to the invention is19,796.7±2 D when analysed by means of MALDI mass spectroscopy and isincreased by 236.7±2 D compared to unmodified hh protein(cytoplasmically expressed hh protein in E. coli), corresponding to themolecular weight of a palmitic acid thioester. The hydrophobicmodification increases the mobility in SDS-PAGE by increased SDS bindingso that apparently a lower molecular weight is seen under alkylatingconditions (derivatized hh protein) than under strongly reducingconditions (hh protein without derivatization). The accuracy of themolecular weight determination in SDS-PAGE is also about ±1-2 D.

After purification with heparin-Sepharose, hydroxyl-apatite and porousHSM ion exchanger chromatography, the hh mutant according to theinvention has an activity measured via the induction of alkalinephosphatase in a cell test (activity in the AP cell test) which isincreased by at least 50-fold, preferably by at least 100-fold andparticularly preferably by at least 10³ to 10⁶-fold compared to solublehh protein expressed in the cytoplasm of E. coli. Such an active hhmutant is not modified by cholesterol like the N-terminal hh fragmentdescribed by J. A. Porter since only the N-terminal and not also theC-terminal autoprocessing domain was expressed. The hh mutant accordingto the invention is present in a biologically active three-dimensionalstructure. Consequently the invention for the first time enables theisolation of highly active hedgehog protein and provides a general,reproducible method for the production and characterization of highlyactive hedgehog proteins.

Hence the invention concerns hedgehog proteins with an at least100-fold, preferably at least 10³ to 10⁶-fold increased activitycompared to the corresponding hedgehog protein which was isolated fromthe cytoplasm of E. coli were the activity is determined by theinduction of alkaline phosphatase in the cell test.

A corresponding hedgehog protein which is produced in the cytoplasm ofE. coli is understood according to the invention as a hedgehog proteinwhich is isolated in a soluble form in the cytoplasm after expression inE. coli. In this process a vector is used as the expression vector whichcontains a nucleic acid to be expressed which codes for a hedgehogprotein of the same amino acid sequence as the nucleic acid to beexpressed of the expression vector which is used for expression in thebaculovirus expression system. However, in this process it may beexpedient to change one or other amino acid in the baculovector or E.coli vector in order to for example improve the expression or thesolubility. However, for the comparison of activities of the hedgehogprotein according to the invention with the E. coli protein it isexpedient to use expression vectors for identical proteins. The hhprotein that is formed in this process is not post-translationallymodified (no derivatization with cholesterol etc.).

The hh mutant according to the invention is very sensitive towardsproteases which is why it is preferable to add protease inhibitors suchas for example aprotinin, EDTA (up to 1 mmol/l), PMSF or pepstatin or amixture thereof to the supernatant of the fermentation.

Furthermore it is preferable to add non-ionic detergents such aspolysorbate (e.g. Tween®20, Tween®80, Triton®X100) during thepurification, preferably before or after the first crude purificationover heparin-Sepharose. Since this also stabilizes the hh proteinsaccording to the invention.

In a first step for the purification of the protein according to theinvention it is expedient to carry out a chromatography onheparin-Sepharose. It is preferable to carry out this chromatography asa step elution i.e. preferably to elute at a concentration of at least0.7 mol/l NaCl (preferably 1.2 mol/l) after washing with 250 mmol/lNaCl.

It is particularly preferable to carry out a hydroxylapatitechromatography to purify the hh mutant according to the invention. Thisachieves a good concentration of the activity with relatively low losses(<50%). Further suitable chromatographic steps are for example aheparin-Sepharose chromatography (Miao et al., J. Neurosci. 17 (1997)5891-5899) which is, however, preferably carried out in the presence ofnon-ionic detergents. Furthermore it is preferable to carry out adialysis after the heparin-Sepharose chromatography in which it isparticularly preferable that in this dialysis the pH value of the bufferis at least pH 5, in particular pH 6.5-7.5 and the ionic strength of thebuffer corresponds to a solution of 1-20 mM sodium phosphate and 10-100mM NaCl in particular 50 mM NaCl and the dialysis is carried out at alow concentration of total protein (1 mg/ml or less, preferably 0.5mg/ml or less).

Furthermore, it is also preferable to add suramin during thepurification or at least before determining the activity of the protein.The activity can also be stabilized by adding serum albumin (at least 50μg/ml to 5 mg/ml) to the sample before dilution in the cell test. Thisalso stabilizes the activity. In the case of suramin it was previouslyonly known that it is suitable for detaching hh proteins from the cellsurface or the extracellular matrix (Bumcrot et al., see above).

Furthermore, it is known that suramin inhibits the activity of growthfactors (Middaugh et al., Biochem. 31 (1992) 9016-9024). Surprisingly itwas found that the activity of hh proteins is increased by addingsuramin.

For the further purification it is preferable to repeat chromatographyon heparin-Sepharose and hydroxylapatite.

For the further purification it is additonally preferable to carry outan ion exchange chromatography with porous HS/M and/or Poros-Q(Boehringer Mannheim GmbH, DE) and preferably subsequently a RP-HPLC. Incontrast to other ion exchanger media, only low losses of activity and agood separation of the active hh form is observed with Poros exchangers.

In a further embodiment of the invention the hh mutant according to theinvention can be used to produce a pharmaceutical composition which isalso a subject matter of the invention. This pharmaceutical compositioncontains a pharmacologically effective dose of the protein according tothe invention and can be administered systemically as well as locally.It is also preferable to use the proteins according to the invention incombination wish other proteins of the hedgehog family or bone growthfactors such as bone morphogenetic proteins (BMPs), (Wozney et al.,Cell. Mol. Biol. of Bone, Bone Morphogenetic Proteins and their GeneExpression, 131-167, Academic Press Inc. 1993) or parathyroid hormones(Karablis et al., Genes and Development 8 (1994) 277-289).

The protein according to the invention can be used advantageously toinduce or stimulate chondrocytes and osteocytes in an osteoinductivepharmaceutical composition as well as to treat neurodegenerativediseases. Osteoinductive pharmaceutical compositions are for exampleknown from the U.S. Pat. No. 5,364,839, WO 97/35607, WO 95/16035.

When the protein according to the invention is administered locally itis preferable to use it in combination with a suitable matrix as acarrier and/or with a sequestering agent. Such a matrix is suitable forslowly releasing the protein in vivo in an active form in particular inthe vicinity of bone and cartilage. The sequestering agent is asubstance which facilitates administration for example by injectionand/or prevents or at least delays migration of the protein according tothe invention from the site of administration.

A biocompatible degradable material for example based on collagen orother polymers based on polylactic acid, polyglycolic acid orco-polymers of lactic acid and glycolic acid are particularly suitableas a matrix material. Such polymer matrices are described for example inWO 93/00050.

Sequestering agents are for example cellulose and cellulose-likematerials and for example alkyl cellulose, carboxymethyl cellulose,hyaluronic acid, sodium alginate, polyethylene glycol and polyvinylalcohol of which hyaluronic acid is particularly preferred especially ina pharmaceutical composition even without carrier matrix.

It is also preferable for the production of the pharmaceuticalcomposition to add auxiliary substances such as mannitol, sucrose,lactose, glucose or glycine and antioxidants such as EDTA, vitamin C,citrate and detergents, preferably non-ionic detergents likepolysorbates and polyoxyethylenes. A pharmaceutical composition which isbuffered in the pH range 4-8 is also preferred.

In a further preferred embodiment a pharmaceutical composition of thehedgehog protein according to the invention together with suramin and/orserum albumin is preferred and this is advantageously used.

The following example, publications and figures further elucidate theinvention, the protective scope of which results from the patent claims.The described methods are to be understood as examples which stilldescribe the subject matter of the invention even after modifications.

EXAMPLE 1 Expression of Recombinant Human Sonic hh (shh)

The N-terminal domain of human shh with the amino acids 24-197 (EMBLaccession No. L 38518) was expressed with the N-terminal signal peptide1-23 as described by Miao (J. Neurosci. (1997) 17, 5891-5899) andBumcrot et al., (Mol. Cell. Biol. (1995) 15, 2294-2303) for the ratprotein by means of recombinant baculovirus in High Five cells(Invitrogen, Leek, N L, Order No. E 855-02) using Excell 400 medium(JHR, Inc.) in which sufficient virus was used to infect each cell onaverage with one virus (multiplicity of infection (m.o.i.):1).

The fermenter contents were clarified after 26 or 72 h by centrifugationat 1000 g and filtration and the supernatant or the permeate was storedat -80° C. until further use. Fermentation samples were analysed fortheir content of alkaline phosphatase inducing activity [Nakamura et al.(1997), Kinto et al. (1997) FEBS Lett. 404, 319-323] and for theircontent of shh protein by means of RP-HPLC (Vydac C18, gradient of 0-90%acetonitrile in 0.1% trifluoroacetic acid, TFA) or SDS-PAGE.

In the preferred process the fermentation was terminated after 24-32 h(preferably after 24-27 h) fermentation time and the supernatant wasclarified.

EXAMPLE 2 Purification of the Active hh Mutant on heparin-Sepharose andhydroxyapatite

1 Tablet of “complete” inhibitor mix (Boehringer Mannheim GmbH, orderNo. 1873580) was added per 50 ml supernatant to the clarifiedsupernatant after thawing and 3.5 l of this solution was applied at 4°C. to a heparin-Sepharose column (volume 90 ml; Pharmacia Biotech) whichhad previously been equilibrated with 20 mM sodium phosphate, pH 7.2.After the sample application it was washed with 20 mM sodium phosphate,0.05% Tween®80, pH 7.2 (=buffer A) and unspecifically bound protein waseluted by a wash step with buffer A which additionally contained 0.25 MNaCl. The activity was obtained by a subsequently elution with buffer Awhich additionally contained 1.2 M NaCl.

This eluate was subsequently diluted with one volume 10 mM sodiumphosphate, 0.05% Tween®80, 50 mM NaCl, pH 7.2 (=buffer B) and dialysedagainst buffer B at 4° C.

The dialysate was applied to a hydroxyapatite column (volume 10 ml;Makro Prep; 40 μm, type I; BIO-Rad) equilibrated with buffer B. It waseluted with a gradient of 10 to 300 mM NaP in buffer B (2×200 ml).

Aliquots of the fractions were analysed for their ability to stimulatealkaline phosphatase in a mouse fibroblast cell line e.g. C3H10T½ cellsas well as by means of SDS-PAGE and RP-HPLC. The remainder of thefractions was stored at −80° C. until further processing. The maximumactivity elutes at the end of the gradient between 0.25-0.3 M sodiumphosphate whereas inactive or only weakly active forms of shh alreadyelute much earlier from the column.

The active fractions were pooled and dialysed against buffer B at 4° C.and applied to a 1 ml HiTrap heparin column (Pharmacia Biotech) whichhad been equilibrated with 20 mM potassium phosphate, 0.05 Tween®80, pH7.2. It was eluted by a gradient of 20-1400 mM KCl in 20 mM potassiumphosphate, 0.05% Tween®80, 50 mM NaCl, pH 7.2. Active fractions wereidentified by the stimulation of alkaline phosphatase in C3H10T½ cells,and alkylated and reduced samples were analysed by means of SDS-PAGE andWestern blot with an antibody against the N-terminus of shh.

EXAMPLE 3 Purification of the Active hh Mutant on a Cation Exchanger andRP.HPLC

(1) Purification by cation exchange chromatography on PorosHS/M:

The active fractions after the hydroxylapatite or HiTrap heparinchromatography of example 1 were pooled and dialysed against 50 mMpotassium phosphate, 0.05% Tween®80, pH 7.2 (=buffer C) and applied to a1.7 ml Poros®HS/M column (Boehringer Mannheim GmbH, GER) which had beenequilibrated in buffer C. It was eluted by a gradient of 40 columnvolumes of 50-1000 mM KCl in buffer C and at a flow rate of 3 ml/min.Active fractions were identified by stimulation of alkaline phosphatasein C3H10T½ cells. The active fractions eluted at a salt concentration ofca. 400-700 mM KCl and the alkylated samples had a purity of ca. 50%; inthe SDS-PAGE under alkylating conditions whereas the major portion ofthe proteins already eluted at a salt concentration of ca. 80-400 mMKCl. It is possible to identify the highly active hh derivativecontained in these fractions by subsequent RP-HPLC and mass analysis ofthe elution peak or by an appropriate analysis of the gel bands in theSDS-PAGE with a molecular weight of ca. 22 kD.

(2) Purification by RP-HPLC:

Active fractions of the Poros®-HS/M chromatography were further purifiedby RP-HPLC. For this 3.2 ml of a highly active fraction was applied to a2.1×150 mm butyl column (Vydac™ 214TP5215) which had been equilibratedin 20% acetonitrile, 0.1% trifluoroacetic acid (TFA). It was eluted at25° C. in a gradient of 20-90% acetonitrile in 0.1% TFA and analysed bydetecting the absorbance at 220 nm and 280 nm. In comparison to weaklyactive unmodified monomeric or dimeric hh forms, the concentrated highlyactive hh derivative did not elute until a somewhat higher concentrationof acetonitrile (ca. 41.2%). This species was collected and its mass wasdetermined by MALDI mass spectrometry.

(3) Mass Analysis of the Active hh Derivative After RP-HPLC

For the mass analysis the RP eluate described above (total volume 200μl) was admixed with 5 μl 25 mM sinapinic acid in 30% (w/w)acetonitrile/70% water/0.1% trifluoro-acetic acid, evaporated to drynessin a Speedvac concentrator and dissolved in 5 μl 30% (v/v)acetonitrile/70% water/0.1% trifluoroacetic acid. 1 μl of the solutionobtained in this manner (referred to as solution A in the following) wasmixed with 1 μl 25 mM sinapinic acid in 30% (v/v) acetonitrile/70%water/0.1% trifluoroacetic acid, applied to the target, dried inlaboratory air and after drying it was measured in a Bruker REFLEX MALDImass spectrometer with a so-called delayed extraction source. Only onemolecular species was detected in the mass spectrum obtained in thismanner apart from alkali and matrix adducts. Since the determination ofthe molecular mass without using an internal standard is only ±0.03%,the mass spectrum of an aliquot of solution A to which a protein of aknown mass had been added was measured in addition to the mass spectrumof the pure solution A. For this 0.5 μl of solution A, 0.5 μl of anequivalently prepared solution of a shortened hedgehog molecule with anaverage molecular weight of 18900.1 D and 1 μl 25 mM sinapinic acid in30% (v/v) acetonitrile/70%. water/0.1% trifluoroacetic acid were mixed,applied to the target, dried in laboratory air and after drying weremeasured by mass spectrometry in the same manner. The spectra obtainedin this manner (FIG. 17) were calibrated with the aid of singly anddoubly charged ions of the molecule used for spiking. The molecularmasses determined for the active hedgehog species present in solution Aare summarized in the following Table 1. TABLE 1 Difference from theMolecular mass of molecular mass of the Spectrum of the active hedgehogunmodified hedgehog FIG. 1/signal molecule molecule (19560.0 D) A/MH⁺19795.6 D 235.6 D A/MH⁺⁺ 19797.6 D 237.6 D B/MH⁺ 19796.3 D 236.3 DB/MH⁺⁺ 19797.2 D 237.2 D

Taking into consideration the inaccuracy of the mass determination of±0.01%, the difference between the molecular mass determined for theactive hedgehog molecule and the molecular mass of the unmodifiedhedgehog molecule is 236.7±2 D. Among the known naturally occurringcovalent protein modifications only esterification with C16 fatty acids(palimitic acid: mass increase by 238.4 D, monounsaturated palmiticacids: mass increase by 236.4 D) leads to an increase of the molecularmass which is compatible with the found increase in mass (Turner andSmith, Molecular Biotechnol. 8 (1997) 233-249).

(4) Purification by Anion Exchange Chromatography on Poros®-Q:

In addition or alternatively to purification by means of cation exchangechromatography on Poros®-HS/M, it is also possible to purify the HA orthe heparin HiTrap eluates by means of anion exchange chromatography onPoros®-Q. For this the active fractions were pooled, dialysed against 20mM Tris/HCl, 0.05% Tween®80, pH 9.0 (=buffer D) and applied to aPoros®-Q column which had been equilibrated in buffer D. It was elutedby a gradient of 60 column volumes of 0-1000 mM NaCl in buffer D. Activefractions were identified by stimulation of alkaline phosphatase inC3H10T½ cells. Active hh protein eluted at a salt content of 90-175 mMNaCl. These active fractions can be further purified and characterizedby means of Poros®-HS/M or RP-HPLC or SDS-PAGE and Western blot asdescribed above.

EXAMPLE 4

Stability of the Active hh Mutant Towards Reducing Agents

(1) Stability Towards dithiothreitol (DTT)

The step eluate of a heparin-Sepharose column containing buffer A whichadditonally contained 1.2 M NaCl (see example 3) was diluted with 1volume 0.05% Tween®80 and 1/10 vol. 1 M Tris/HCl, pH 8 was added for thesamples at pH 8. DTT was added to the samples at final concentrations of0 mM, 1 mM, 10 mM and 50 mM. After 2 h incubation at 37° C., each of thesamples was admixed with 1/10 volumes (50 μl) 10 mg/ml BSA and dialysedagainst PBS. Before use in the C3H10T½ cell test, a final concentrationof 0.1 mg/ml suramin was added to each sample in order to stabilize theremaining activity.

It turned out that the activity at pH 7.2 is stable up to aconcentration of 10 mM DTT, however, at pH 8 treatment with 1 mM DTTalready leads to a considerable reduction of activity. Such a pHdependency would be expected for the reduction of sulphur in disulfidebridges as well as of thioesters of fatty acids (Issartel et al., Nature351 (1991) 759-761).

(2) Stability Towards hydroxylamine (HA):

The step eluate of a heparin-Sepharose column with buffer A whichadditionally contained 1.2 M NaCl (see example 3) was adjusted with NaOHto pH 8.0 or with HCl to pH 5.5. Aliquots of these samples were eachadmixed with 0 mM, 66 mM, 250 mM or 1 M of NH₂OH with the correspondingpH value and incubated for 14 h at RT. The samples were subsequentlydialysed against 20 mM NaP, 250 mM NaCl, 0.05% Tween80, pH 7.4 andadmixed with 1 mg/ml (final concentration) BSA and 0.1 mg/ml (finalconcentration) suramin before analysis in the cell test.

It turned out that the activity at pH 5.5 is stable up to 66 mM HA buttreatment with 66 mM HA at pH 8 already led to a considerable reductionof activity. Such a pH dependency would be expected for the cleavage ofthioesters but not for hydroxyl esters of fatty acids (Issartel et al.,Nature 351 (1991) 759-761; Maggee et al., EMBO J. 4 (1985) 1137-1144).

EXAMPLE 5

Induction of Alkaline Phosphatase in the Cell Test (Determination of theActivity of Alkaline Phosphatase)

5000 cells of the murine mesenchymal pluripotent line: C3H10T½ (ATCCCCl-226) were sown in each well of a 96-well microtitre plate. The cellswere in 100 μl DMEM, 2 mM glutamine, 100 IU/ml penicillin, 100 μg/mlstreptomycin and 10% foetal calf serum, FCS. On the next day the activesubstances to be examined were added at the appropriate concentrationsin a volume of 100 μl after 20-500-fold predilution in culture medium.The test was stopped after 5 days. For this purpose the supernatantswere discarded and the cells were washed once with PBS. The cells werelysed in 50 μl 0.1% Triton®X-100 and frozen at −20° C. After thawing 25μl was used for the protein determination and 25 μl for thedetermination of the activity of alkaline phosphatase.

Protein Determination According to the Instructions of the ManufacturerPierce:

75 μl distilled H₂O was added to the mixture, then 100 μl BCA proteinreagent was added (Pierce Micro BCA, No. 23225). After 60 min theoptical density (OD) at 550 nm was measured.

Activity of the Alkaline Phosphatase According to the Instructions ofthe Manufacturer Sigma:

100 μl reaction buffer (Sigma 221) was added to the preparation. Asubstrate capsule (Sigma 104-40) was dissolved in 10 ml redistilled H₂Oand then 100 μl was added to the test mixture by pipette. The OD wasmeasured at 405 nm after the yellow coloration. In the reaction alkalinephosphatase converts p-nitrophenyl phosphate into p-nitrophenol.

The ODs were each converted into nmol or μg by means of standard curves.The evaluation was according to the formula:

nmol PNP per (measured) minute per mg (cell) protein

EXAMPLE 6

Comparison of the Specific Activities of Unmodified hShh from E. coliwith the hShh Derivative Purified from BVCM

In order to compare the specific activities of the diverse hh forms, hhprotein was used at a defined concentration in the C3H10T½ cell test. Inthis case the protein determination was carried out for the unmodifiedhh protein from E. coli by means of its UV absorbance at 280 nm (Mach,H., et al., Anal. Biochem. 200 (1992) 74-80). The concentration of thehh derivative purified from the baculovirus fermentation supernatant wasdetermined by means of RP-HPLC. The concentration in the stock solutionwas determined by integrating the area under the absorbance curve of thehh peak in the RP-HPLC where the detection was carried out at 220 and280 nm and a calibration curve was established by an analogouschromatography using stock solutions of unmodified shh of knownconcentration. The relative activity of the isolated shh proteins wasdetermined in the C3H10T½ cell test by determining the stimulation ofthe expression of alkaline phosphatase in these cells (example 5; celltest) compared to the baculovirus fermentation supernatant (BVCM after24 hour fermentation) in a 1:40 dilution where the individual valueswere corrected for the base line activity of the cells in the absence ofadded shh. This determination of the relative activity is preferredsince the stimulatability of the cells is influenced by the medium usedand the preculture of the cells.

Table 2 shows the relative activities of purified, unmodified shh fromE. coli and of the shh derivative purified from the supernatant of thebaculovirus fermentation supernatant, which had been purified bychromatography on heparin-Sepharose, hydroxylapatite and Poros HS/M.

As shown in Table 2, hh protein purified from E. coli must be present ata concentration of ca. 240 μg/ml but the hh protein derivative onlyneeds to be present at a concentration of ca. 2.3 ng/ml in the cell testin order to reach the same alkaline phosphatase activity as the BVCM ata 1:40 dilution. Thus the hh protein derivative has a ca. 10⁴-10⁵-foldhigher specific activity than the unmodified hh protein. TABLE 2 Hh Hhconcentration Dilution concentration relative AP of the stock in the inthe cell inducing Hh source solution cell test test activity BVCM  12μg/ml 1:40 0.3 μg/ml 1 Poros HS/M 0.56 μg/ml   1:100 5.6 ng/ml 2.4purified hShh derivative Unmodified 860 μg/ml 1:20 43 μg/ml 0.18 hShhmonomer from E. coli Buffer control — 1:40 — 0

EXAMPLE 7

in vivo Activity of palmitoylated hh

The in vivo activity of modified and unmodified shh protein was examinedin an animal model established for bone growth factors (Mackie &Trechsel, Bone 11 (1990) 296; Kling, L., et al., J. Bone Min. Res. 11(Suppl. 1) (1996) 153). Seven week old female BALB/c mice weresubcutaneously injected daily over a period of 15 days with 1, 10 or 50μg shh in a volume of 50 μl into the cranial calotte. 14 days aftercompletion of the treatment, the calottes were removed and purified ofsurrounding connective tissue. Subsequently the weights of thestandardized explants and the X-ray density were analysed. Modified shhexhibited a higher osteoanabolic effect than unmodified shh.

EXAMPLE 8

Influence of trypsin and chymotrypsin on the Activity of shh

After step elution of heparin-Sepharose the AP active fractions wereadmixed with trypsin or chymotrypsin at different protease/proteinratios. After incubation of the samples for 20 h at 25° C. the digestionwas stopped by addition of aprotinin and the samples were analysed bymeans of SDS-PAGE and in the C3H10T½ test (see FIG. 11).

It turned out that the hedgehog protein is degraded to a shortened formwhich migrate at 20 kDa in the SDS-PAGE. By means of amino-terminalsequencing and MALDI mass spectrometry it could be shown that the maturehh protein is degraded by the chymotrypsin or trypsin treatment at aprotease/protein ratio (w/w) of 1:100 to fragments in which the first 7or 14 amino-terminal amino acids are absent. As shown by the-results ofthe C3H10T½ test in FIG. 11, the alkaline phosphatase inducing activityis also reduced when the hh protein is shortened.

LIST OF REFERENCES

-   Asahina, J., Exp. CeII. Res. 222 (1996) 38-47-   Bitgood, M. J. et al., Curr. Biol. 6 (1996) 296-   Bumcrot et al., Mol. Cell. Biol. 15 (1995) 2294-2303-   Cha et al., Proc. Natl. Acad. Sci. USA 94 (1997) 10577-10582-   Chiang, C. et al., Nature 83 (1996) 407-   Fietz., M. et al., Development (Suppl) (1994) 43-51-   Hynes, M. et al., Neuron 15 (1995) 35-44-   Issartel et al., Nature 351 (1991) 759-761-   Karablis et al., Genes and Development 8 (1994) 277-289-   Kinto et al., FEBS Letters, 404 (1997) 319-323-   Kling et al., J. Bone Miners. 11 (Suppl. 1) (1996) 153-   Lai, C. J. et al., Development 121 (1995) 2349-   Mach, H., et al., Anal. Biochem. 200 (1992) 74-80-   Mackie & Trechsel, Bone 11 (1990) 296-   Maggee et al., EMBO J. 4 (1985) 1137-1144-   Miao et al., J. Neurosci. 17 (1997) 5891-5899-   Middaugh et al., Biochem 31 (1992) 9016-9024-   Nakamura, T. et al., Biochem. Biophys. Res. Comm. 237 (1997) 465-469-   Perrimon, N., Cell 80 (1995) 517-520-   Porter, J. A. et al., Science 274 (1996) 255-259-   Smith, J. C., Cell 76 (1994) 193-196-   Turner and Smith, Molecular Biotechnol. 8 (1997) 233-249-   U.S. Pat. No. 5,364,839-   Vortkamp, A. et al., Science 273 (1996) 613-   WO 97/35607-   WO 93/00050-   WO 95/16035-   Wozney et al., Cell. Mol. Biol. of Bone, Bone Morphogenetic Proteins    and their Gene Expression, 131-167, Academic Press Inc. 1993

1. A protein in isolated form wherein said protein comprises a humanhedgehog protein which is esterified at the N-terminal domain with afatty acid having from 14 to 20 carbon atoms, said protein having amolecular weight of from about 19 to about 26 kD.
 2. The protein ofclaim 1, wherein the fatty acid is palmitic acid.
 3. The protein ofclaim 2, wherein the amino acid sequence of said protein is at least 80%homologous with the amino acid sequence of EMBL database sequence No.L38518.
 4. The protein of claim 3, wherein said protein contains theamino acid sequence of EMBL database sequence No. L38518.
 5. The proteinof claim 3, wherein the protein is esterified at a cysteine residue atthe N-terminal domain of said sequence.
 6. A method for producing ahedgehog protein esterified with a fatty acid having from 14 to 20carbon atoms comprising: a) providing an insect cell in a medium, saidmedium and said insect cell being capable upon fermentation of producinga fatty acid having from 14 to 20 carbon atoms, said insect cellcontaining a baculovirus vector having a gene inserted therein capableof expressing a hedgehog protein; b) fermenting said insect cell in saidmedium for a period of about 30 hours or less to produce the fatty acidand-express the hedgehog protein esterified with said fatty acid; and c)isolating said esterified hedgehog protein from the protein producedduring said fermentation.
 7. The method of claim 6,.wherein thefermentation period of said host cell is from about 24 hours to about 27hours.
 8. The method of claim 6, further comprising isolating saidesterified hedgehog protein in the presence of a protease inhibitor anda non-ionic detergent.
 9. The method of claim 6, further comprisingisolating said esterified hedgehog protein in the presence of suramin.10. Post-translationally processed hedgehog protein mutant which isobtainable by expressing a gene which codes for a hedgehog protein in abaculovirus expression system in a fermentation for a period of up to 30hours, purifying the cell supernatant in the presence of a proteaseinhibitor and a non-ionic detergent and isolating the hh mutant whichbinds to heparin-Sepharose and hydroxylapatite and is characterized inthat this hh mutant exhibits a molecular weight of 22±2 kDa underalkylating conditions, exhibits a molecular weight of 24±2 kD underreducing conditions, is stabilized with respect to its activity bysuramin is inactivated when 8 or more amino acids are cleavedN-terminally is inactivated by 90% or more when incubated with 10 mmol/lDTE for 2.5 hours at 37° C., induces an activity for alkalinephosphatase of ca. 90 nmol pNP/min/mg at a concentration of 5 nmol/l inthe presence of suramin, is not modified by cholesterol and has an atleast 50-fold activity compared to the recombinant hh protein isolatedfrom the cytoplasm of E. coli.
 11. Process for the production of apost-translationally processed hedgehog protein mutant by expressing agene which codes for a hedgehog protein in a baculovirus expressionsystem in a fermentation for a period of 24 to 27 hours, purifying thecell supernatant in the presence of a protease inhibitor and a non-ionicdetergent and isolating the hh mutant which binds to heparin-Sepharoseand hydroxylapatite and characterized in that this hh mutant exhibits amolecular weight of 22±2 kDa under alkylating conditions, exhibits amolecular weight of 24±2 kD under reducing conditions, is stabilizedwith respect to its activity by suramin is inactivated when 8 or moreamino acids are cleaved N-terminally is inactivated by 90% or more whenincubated with 10 mmol/l DTE for 2.5 hours at 37° C., induces anactivity for alkaline phosphatase of ca. 90 nmol pNP/min/mg at aconcentration of 5 nmol/l in the presence of suramin, is not modified bycholesterol and has an at least 50-fold activity compared to therecombinant hh protein isolated from the cytoplasm of E. coli. 12.Process as claimed in claim 11, wherein, after chromatography onheparin-Sepharose, it is dialysed against lower ionic strengths. 13.Process as claimed in claim 12, wherein the dialysis is carried out inthe presence of 10-100 mmol/l sodium chloride.
 14. Pharmaceuticalcomposition containing a hh mutant as claimed in claim
 10. 15.Pharmaceutical composition as claimed in claim 14, containing suramin,serum-albumin, a biocompatible matrix and/or a sequestering agent. 16.Process for the production of a pharmaceutical composition bycombination of a hh mutant as claimed in claim 10 with a pharmaceuticalauxiliary substance or with suramin.
 17. Process for the production of apharmaceutical composition by combination of a hh mutant as claimed inclaim 10 with a biocompatible matrix and/or a sequestering agent. 18.Post-translationally processed hedgehog protein with an at least 50-foldhigher activity than the hedgehog protein expressed cytoplasmically inE. coli.
 19. Pharmaceutical composition containing a hedgehog protein asclaimed in claim
 18. 20. Process for the production of a pharmaceuticalcomposition, wherein a hedgehog protein as claimed in claim 18 is usedas an essential component of this pharmaceutical composition.